Chromatography has been suggested for the interseparation of platinum group metals (“PGM”—platinum, palladium, rhodium, osmium, ruthenium and iridium). The earliest suggestion was in U.S. Pat. No. 4,855,143. However, it was found that the media recommended therein exhibited serious degradation in the concentrated acid necessarily used for solutions of the PGM. Later, U.S. Pat. No. 5,879,644 taught the use of selected commercial media, especially “Toyopearl”, for the interseparation of the PGM. These, especially when combined with certain process improvements, provided good separation and beneficial lifetimes however, capacity was found to be low and high volumes of eluant were required leading to increased costs. The chromatographic separation process appears to offer great promise for PGM refining. There remains, however, the need for further improved media, especially for the recovery or separation of palladium. Very many commercial media have been tested but none has exhibited the desired combination of properties namely, increased throughput and good metal separation per unit volume of eluant.
The use of solid phase extraction is commonplace in PGM separation and refining. For example, the use of specified thioethers has been recommended for the extraction of Pd from nitric acid solutions of plutonium arising from the nuclear industry (U.S. Pat. No. 5,171,546). U.S. Pat. No. 4,959,153 proposes the binding of thioether-based materials linked to silica, and we believe that these have been introduced into commercial PGM refining processes and are marketed as “Superlig”. Such solid phase extractant materials demonstrate fast binding of Pd but, the use of an inorganic support (silica) means that their capacity is rather low, and tests have shown almost halving of capacity after three month's use.
Sulphur containing groups have been used as cross-linkers to provide solvent stability to polysaccharide and oligosaccharide materials, US 2001/0029282 A1. The cross-linked polymers are useful for the separation of chiral enantiomers.
EP 0 608 703 also relates to materials useful in the separation of mixtures of organic compounds such as racemates. The materials comprise a cyclodextrin species attached to a support via an intermediate group which may be sulphur containing. It is the cyclodextrin species which is active in the separation process.
EP 0 355 376 relates to media for the extraction of metal ions from solution. The media are composed of an inorganic silica support onto which organic sulphur containing groups may be attached.